The present invention relates to the manufacture of fibrous glass mat products and more specifically to that class of mat products known as "continuous mat." Such mats are manufactured by the deposition of continuous strands of glass fibers onto a foraminous conveyor or collection surface, the strands being deposited in overall sinuous configuration with laterally adjacent strands overlapping one another. The overall method of making such mats is well illustrated in U.S. Pat. No. 3,760,458, assigned to the assignee of the present invention. This patent illustrates the former commercial method of making continuous strand mats, and the present invention provides a specific improvement over the process and apparatus disclosed in said patent.
Typically, in a commercial operation, each strand contains 24 filaments and 360 strands are laid down in an overlapping sinuous pattern to provide a 3 foot wide mat.
In a mat of this character, the individual strands are intermingled and overlapping, but it is necessary to disperse the individual filaments of the strands so that the intermingling of the dispersed filaments is also obtained. It is this intermingling and mechanical adherence between the individual filaments, when tied together by the cured binder which gives the mat its commercially useful characteristics of (1) high strength and (2) small, uniform interstices.
In commercial practice, the foraminous conveyor travels at high speeds, on the order of 180 to 300 feet per minute and the primary orientation of the sinuous strands is longitudinally of the rapidly traveling conveyor. It is necessary to separate and disperse individual filaments from each strand while still retaining the overall sinuous configuration of the strands in order to provide both the high strength and the small, uniform interstices required in mats of this type.
This dispersion of the filaments was accomplished in the prior art, as typified by the disclosure U.S. Pat. No. 3,760,458 by flooding the strands on the conveyor with a liquid preferably containing the binder, retaining the strands in their flooded condition for a period of time sufficient to overcome the forces holding the filaments together in the strands and then draining the flooding liquid preparatory to heat curing the mat impregnated with binder.
The resultant prior art mat, of a density of 0.0225 pounds per square foot, had appreciable longitudinal tensile strengths, on the order of 150 pounds per square inch, but was of relatively low transverse strength, generally about 80 to 90 pounds per square inch. Further, the interstices of the prior art mat were not uniform and were relatively large particularly in the longitudinal direction. If it were possible to increase the transverse strength of continuous strand mats and to provide more uniform, smaller interstices therein, a more desirable commercial product could be obtained.